Gamerscores and Achievement lists being reset to zero.

Xbox Live users have reported Gamerscores and Achievement lists being reset to zero. Microsoft has said it is aware of the issue and notes: We are aware of the problem and appreciate your patience while we implement a solution.

I know the article doesn't mention it, but this particular issue also affects avatar awards.

Edit:

Hey guys, thank you all for posting in this thread. I want to let you know that we're aware of an issue with achievements, and that we're doing everything we can to resolve it ASAP. At this time, we believe the issue should be resolved. If you're missing achievements, please try signing out of Xbox LIVE, then sign back in. If this doesn't resolve your issue, then you will need to re-download your profile. Please note that this will remove any achievements you might have earned since the issue began, however, they can be re-earned